1. Field
The present invention relates generally to ink jet printers, and particularly, to ink jet printers that use a recirculating ink supply.
2. Description of the Problem and Related Art
In an inkjet printer drops of ink are jetted out of nozzles of an inkjet printhead towards a receiving layer which may be e.g. specially coated paper. Usually an inkjet print head has an array of nozzles, each nozzle jetting ink to a different location possibly at the same time. The ink is jetted out of the nozzles by use of e.g. thermal or piezoelectric actuators creating a pressure wave. It is normally the intention that the size of the droplets can be kept constant or that there is a good control of the droplet size in printers capable of recording variable droplet sizes. One of the major parameters to ensure a constant drop size is that ink pressure at the printhead is stable and within a certain range suitable for the printhead used.
Ink pressure at the printhead nozzle can be kept constant using several methods. For example, small inkjet printers often employ a negative pressure generating member present in the ink reservoir mounted on the shuttle carrying the printhead. In larger printers and industrial inkjet printers an ink tank is often equipped with a system regulating and stabilizing the pressure in the tank by directly controlling the ink pressure or the pressure of the air (atmosphere) above the ink.
Another recurring issue prior designs must overcome is pressure fluctuations which result in non-uniform droplet size, decreasing the quality of the print. Such pressure fluctuations can be produced by diaphragm or impeller ink pumps. Prior systems attempt remediate these pressure fluctuations or pulses by adding pressure regulating components, resulting in large, complex and cumbersome systems. In particular, pulsing is exacerbated in large scanning printhead applications where the print media is large and the printhead traverses the media as it deposits ink thereon where the printhead is mounted to a carriage controlled by the printer system. These large prior art systems incorporate a recirculation tank (sometimes two), filters, pumps and heaters which must remain stationary because the carriage cannot bear the load scan practically. Consequently, the ink supply system must be connected to the printhead with long tubes and each time the printhead carriage stops and starts during a print job, a pressure pulse is generated in the tubes and is transmitted to the printhead. Additionally, long ink supply and return tubes mean significant thermal losses which conventional systems attempt to remediate with additional heating. However, this can result in overheating of UV curable inks which can promote premature curing and contribute to chemical instability.